Tubular batteries such as cylindrical or prismatic batteries are sealed, e.g., by inwardly crimping the open end portion of a bottomed tubular battery case to compress an insulating gasket, thereby providing liquid-tight sealing between the battery case, the insulating gasket, and a sealing member. However, even a trace amount of electrolyte deposited on the sealed portion or an imperfect sealing itself would cause the interface between two components in the sealing structure to be wetted with the electrolyte. This may lead to the development of a leakage path, resulting in leakage occurring by the electrolyte migrating along the leakage path. In particular, in those batteries with an alkaline electrolyte, the alkaline electrolyte itself migrates along the surface of the negatively charged metallic sealing member or battery case. Leakage is thus more likely to happen in these batteries when compared with other types of batteries.
Conventionally, to check for the occurrence of leakage, a given number of tubular batteries were arranged side by side with their sealed end faces oriented upwardly. The sealed end face of each tubular battery was then covered with a cloth, to which a reagent was then applied. While the cloth was being tapped with a brush, the tubular battery whose yellow reagent discolored purple was visually identified and determined to be leaky. However, such inspection means that relies on operators' manual operations and visual determinations is limited in terms of the handling speed and thus very inefficient. The inspection is also likely to be inaccurate because variations exist among individual operators and they may overlook leakage. To be worse, such a leakage that occurs immediately inside the sealed end face cannot be visually identified.
In this context, such inspection means has been recently adopted which allows for determining occurrence of leakage by X-ray fluorescence analysis. According to a first one of those conventional techniques, a primary X-ray having a certain pre-defined wavelength is used to irradiate a tubular battery, and a fluorescent X-ray coming out of the tubular battery is allowed to be incident upon an analyzer. The analyzer analyzes whether the incident fluorescent X-ray contains such a fluorescent X-ray that has a wavelength associated with an electrolyte component. Then, based on the output from the analyzer, occurrence of leakage is determined (for example, see Patent Document 1).
On the other hand, according to a second conventional technique, while tubular batteries are being fed in a row at predetermined intervals, each tubular battery is irradiated with an X-ray from an X-ray source. Those fluorescent X-rays arising from the sealed end face and a side of a tubular battery are allowed to be incident upon a plurality of detectors located around the X-ray source. Based on the results of detections provided by the plurality of detectors, a tubular battery with the electrolyte deposited thereon is identified (for example, see Patent Document 2).
[Patent Document 1] Japanese Patent Laid-Open Publication No. Sho 52-138627
[Patent Document 2] Japanese Patent Laid-open Publication No. Hei 9-203714